Like many great stories, the animated documentary “Waltz With Bashir” begins with two men in a bar. It’s a few years ago, and Israeli filmmaker Ari Folman is sitting talking to Boaz, his old pal, now a successful accountant in his 40s. Boaz tells of a recurring nightmare he’s had for 20 years. In the dream, ferocious dogs — 26, to be precise — are racing through town, destroying everything that gets in their way. Their destination? Boaz’s window.